diff --git a/synapse/appservice/api.py b/synapse/appservice/api.py
index cc4af23962..b0eb0c6d9d 100644
--- a/synapse/appservice/api.py
+++ b/synapse/appservice/api.py
@@ -32,6 +32,14 @@ HOUR_IN_MS = 60 * 60 * 1000
 APP_SERVICE_PREFIX = "/_matrix/app/unstable"
 
 
+def _is_valid_3pe_metadata(info):
+    if "instances" not in info:
+        return False
+    if not isinstance(info["instances"], list):
+        return False
+    return True
+
+
 def _is_valid_3pe_result(r, field):
     if not isinstance(r, dict):
         return False
@@ -162,11 +170,18 @@ class ApplicationServiceApi(SimpleHttpClient):
                 urllib.quote(protocol)
             )
             try:
-                defer.returnValue((yield self.get_json(uri, {})))
+                info = yield self.get_json(uri, {})
+
+                if not _is_valid_3pe_metadata(info):
+                    logger.warning("query_3pe_protocol to %s did not return a"
+                                   " valid result", uri)
+                    defer.returnValue(None)
+
+                defer.returnValue(info)
             except Exception as ex:
                 logger.warning("query_3pe_protocol to %s threw exception %s",
                                uri, ex)
-                defer.returnValue({})
+                defer.returnValue(None)
 
         key = (service.id, protocol)
         return self.protocol_meta_cache.get(key) or (
diff --git a/synapse/handlers/appservice.py b/synapse/handlers/appservice.py
index b440280b74..88fa0bb2e4 100644
--- a/synapse/handlers/appservice.py
+++ b/synapse/handlers/appservice.py
@@ -176,12 +176,41 @@ class ApplicationServicesHandler(object):
         defer.returnValue(ret)
 
     @defer.inlineCallbacks
-    def get_3pe_protocols(self):
+    def get_3pe_protocols(self, only_protocol=None):
         services = yield self.store.get_app_services()
         protocols = {}
+
+        # Collect up all the individual protocol responses out of the ASes
         for s in services:
             for p in s.protocols:
-                protocols[p] = yield self.appservice_api.get_3pe_protocol(s, p)
+                if only_protocol is not None and p != only_protocol:
+                    continue
+
+                if p not in protocols:
+                    protocols[p] = []
+
+                info = yield self.appservice_api.get_3pe_protocol(s, p)
+
+                if info is not None:
+                    protocols[p].append(info)
+
+        def _merge_instances(infos):
+            if not infos:
+                return {}
+
+            # Merge the 'instances' lists of multiple results, but just take
+            # the other fields from the first as they ought to be identical
+            # copy the result so as not to corrupt the cached one
+            combined = dict(infos[0])
+            combined["instances"] = list(combined["instances"])
+
+            for info in infos[1:]:
+                combined["instances"].extend(info["instances"])
+
+            return combined
+
+        for p in protocols.keys():
+            protocols[p] = _merge_instances(protocols[p])
 
         defer.returnValue(protocols)
 
diff --git a/synapse/rest/client/v2_alpha/thirdparty.py b/synapse/rest/client/v2_alpha/thirdparty.py
index 4f6f1a7e17..dca615927a 100644
--- a/synapse/rest/client/v2_alpha/thirdparty.py
+++ b/synapse/rest/client/v2_alpha/thirdparty.py
@@ -42,6 +42,29 @@ class ThirdPartyProtocolsServlet(RestServlet):
         defer.returnValue((200, protocols))
 
 
+class ThirdPartyProtocolServlet(RestServlet):
+    PATTERNS = client_v2_patterns("/thirdparty/protocol/(?P<protocol>[^/]+)$",
+                                  releases=())
+
+    def __init__(self, hs):
+        super(ThirdPartyProtocolServlet, self).__init__()
+
+        self.auth = hs.get_auth()
+        self.appservice_handler = hs.get_application_service_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, protocol):
+        yield self.auth.get_user_by_req(request)
+
+        protocols = yield self.appservice_handler.get_3pe_protocols(
+            only_protocol=protocol,
+        )
+        if protocol in protocols:
+            defer.returnValue((200, protocols[protocol]))
+        else:
+            defer.returnValue((404, {"error": "Unknown protocol"}))
+
+
 class ThirdPartyUserServlet(RestServlet):
     PATTERNS = client_v2_patterns("/thirdparty/user(/(?P<protocol>[^/]+))?$",
                                   releases=())
@@ -92,5 +115,6 @@ class ThirdPartyLocationServlet(RestServlet):
 
 def register_servlets(hs, http_server):
     ThirdPartyProtocolsServlet(hs).register(http_server)
+    ThirdPartyProtocolServlet(hs).register(http_server)
     ThirdPartyUserServlet(hs).register(http_server)
     ThirdPartyLocationServlet(hs).register(http_server)